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MG Midget and Sprite Technical - Oversteer

Got a 1500 and I've just changed to 14" alloys with 165 60 14's after running standard 145's for a few weeks. Before that I was running on 165 65 13's. Standard suspension but all shocks and joints very recent and very good apart from maybe the top front trunnion rubbers and rear spring inserts.
With the new tyres/wheels it really does feel like its on rails, especially when powering though big bends or roundabouts. BUT when you lift off in a sharp bend the oversteer is SERIOUS. Its much worse than on the 145's and although I did notice it on the 165 13s but it wasn't this bad.
I don't want to start major suspension mods ahead of the impending K conversion so what would be the first (and not too dear) thing to look at, adjust or do?
Alan McKewan

Try different tyre pressures to start with. Bigger tyres should probably mean lower pressures. As it's easy to do its worth trying anyway.
john payne

probably after air pressure would be a rear pan hard rod. That will keep the axle from moving side to side

But being your moving to a K series, I ld stay with your set up and just do air pressure adjustment

Your suspension will need a big over haul is done because of the weight transfers, plus you will probably want to upgrade brakes as well

A meaner engine will need a beefer suspension and some smokin bigger brakes

But id plan on a pan hard rod and ladder bars in the rear at least, and a bigger ARB rod in the front and alloy wheels all around and a big brake kit, as in MGB calipers on spitfire rotors. You would certianly benifit from reinforced wishbones and a frontline tube shock conversion on the front

Plus uprated rear axle shafts or a revamped complete rear end that can handle the extra power.

But id think you would want to do that after the new K seris is installed

Prop and the Blackhole Midget

Hmm pressure is probably 25+ all round so first step there.
Many moons ago when I previously had a midget or two a mate used to have one for autotesting. I seem to remember that he used to set the toe-in wrong on purpose to induce oversteer to throw the back out. Anyone aware of this or which way to go?
Alan McKewan

Ummm... why are you lifting off the throttle in a sharp bend?
Trevor Jessie

Badger,child, pheasant etc...

Check spring u bolt tightness and condition of rear shackle bushes, all should be pretty good - I've got poly ones on mine and they're great.

Do a quick tracking check too, though if it doesn't feel twitchy on turn in then it's probably pretty close. I seem to remember that to much toe in makes the front grabby, though that may well be the wrong way round..
Rob Armstrong

What is the maskers recommended pressure, surely not 25?
R W Bowers

on std tyres it's 24 F and 28 R, try that.
But bear in mind you have reduced the sidewall height by 25% which is a major change so it's hardly surprising that the effect on the handling is very noticeable. What was your thinking behind moving to 14" wheels?
David Smith

Rule #1 -- Never ever back off the throttle - hahaha

willy

William Revit

Seriously, if you release the throttle too quick you have engine braking. That can cause a loss of traction on the rear tires and then the back steps out. I suspect it is a difference in tire design/compound and not a size/setup issue.

I'd rather have a tad bit of oversteer than understeer.
Trevor Jessie

Read this.

http://www.drivingfast.net/car-control/oversteer.htm

And this for understeer.

http://www.drivingfast.net/car-control/understeer.htm
Lawrence Slater

I've only ever had engine braking instigated oversteer once, due to a very ill timed downchange on corner entry under braking while following a mini.

I'd be surprised if you could instigate oversteer in a healthy properly set up spridget just by lifting off unless you were doing a billion revs or something else was wrong.

Mines set up to be slightly leery with very little understeer, cos I don't like it.
Rob Armstrong

Maybe engine braking alone won't cause oversteer in the corner, but if you're on the limits of the cars holding ability and you lift the throttle suddenly in mid corner the weight transfer can cause the back to step out. I'm not a racer, but I've had a few driving lessons and learned this the hard way.

I have a midget that understeers and a sprite that oversteers. I prefer the sprite, but I prefer that mywife drives the midget since she has primarily driven modern front wheel drive cars with understeer.
Trevor Jessie

What is commonly called 'lift off oversteer' is very common in rear-drive cars and, as has been said, is caused by engine braking and loss of traction. Tyre pressures will make a difference but a panhard rod won't because the problem is not really caused by a lack lateral location; 1970s to 1980s BMWs were massively prone to the problem and their independent and very well located independent rear suspensions did not solve it, perhaps because there was a lot of compliance in the bushings. But, things are made much worse by poor fore-aft location and soft or worn bushes. So radius arms or trailing arms will lessen the problem as will new spring-eye bushes. But lift-off oversteer will always be present in any rear-drive car with a nice snappy off-throttle response, it will never go away entirely.
Nick Nakorn

In the dim and distant past, I ran my mildly tuned Midget on 155/13 tyres on standard Rostyles. Enjoyable oversteer on demand.

Then I fitted a set of 5J rim alloys and 186/70 tyres. Not a big jump I have to admit but the result was interesting.

I found there was more lift off oversteer and generally more sliding when "making progress". I was disapointed having spent all that money to get what appeared to be inferior performance.

Then I noticed I was a gear higher virtually everywhere. The local roundabout was now taken in a very torquey area of third rather than screaming in second.

The lift off oversteer was the result of simply going a lot faster - the weight transfer was greater, along with the heart rate. A 1500 is more prone to any how due to the increased weight and height so the bigger grippier tyres Alan has fitted will amplify the problem - if it is, indeed, a problem. ;)
Clive Berry

AHA after playing with the pressures (now 22 all round) I realise you are right Clive, if I do a roundabout similarly to previously in 2nd on the skinny 145s the lift-off oversteer is much the same, but now I can do 3rd no problem, just need to keep the juice on. BTW a higher rear pressure does make it worse. Also my rear spring bushes are shot and I can feel the axle moving noticeably when the power comes off (or on) on a bend. No point taking out the springs for new bushes without fitting a panhard so the list gets bigger..
Alan McKewan

Alan, if the axle is moving it's usually the pads between spring and axle that are the culprit. Test by driving along a straight bit of road and going power=on, power-off alternately. The car should remain straight, if it shuffles one way and the other each time then it's definitely spring pads. They are a cheap and easy fix, bets to do ASAP if they are a problem.

BTW lift off oversteer in a corner sets in well before there is any loss of traction in the sense that the wheels lock briefly. What does happen is that the slip angles increase at the back, hence the oversteer. It's a very handy effect provided it's not excessive - and a lot of fun at times. Stiffer rear shocks will add to the effect at initial turn in, softer shocks reduce it.
Paul Walbran

This thread was discussed between 25/08/2014 and 31/08/2014

MG Midget and Sprite Technical index

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